1. Field of the Invention
The present invention relates generally to a magnetic recording medium and a magnetic recording drive, and more particularly to a magnetic recording medium composed of a Cr layer and a CoCrPt type alloy film arranged on the Cr layer and a magnetic recording drive having the magnetic recording medium.
2. Description of the Prior Art
In a field of a magnetic disk drive, a magnetoresistive effect type magnetic head (hereinafter, called an MR head) is put to practical use in place of a magnetic induction type magnetic head, and the MR head has been recently used for a magnetic recording drive.
In cases where the MR head is used, magnetic recording information can be detected at a higher sensitivity as compared with the use of the magnetic induction type magnetic head, and superior reproduction characteristics in a band region extending to a high frequency band can be obtained. However, because a medium noise is also detected to a high degree, a signal-to-noise ratio (S/N ratio) in the magnetic disk drive deteriorates.
Also, because the recording in a high recording density is required, a magnetic recording medium is required to have a high coercive force (Hc) on condition that a Br.multidot.t value is low. The Br.multidot.t value is defined as a product of a residual magnetic flux density (Br) in a magnetic recording medium layer and a thickness (t) of the magnetic recording medium layer. As a material having a high coercive force, the use of a CoCrPt alloy is expected. In cases where a medium made of only the CoCrPt alloy is used, a medium noise occurs to a high degree. Therefore, in cases where a CoCrPt alloy type medium is used as a magnetic recording medium, it is required to extremely reduce the medium noise by changing a structure of the magnetic recording medium for the purpose of improving the signal-to-noise ratio in the recording disk drive.
To produce a magnetic recording medium satisfying the above request, a literature (1) "Yang et al., IEEE, Mag-27(1991) 5052" is reported. In the literature, an idea that a CoCrPt type medium layer and a Cr layer having a thickness of about 3 nm are alternately arranged to reduce a medium noise of a medium while maintaining the coercive force to a high value is disclosed.
However, a Br.multidot.t value of the medium in the literature (1) is about 200 G.mu.m, and the improvement of the medium is required to apply the CoCrPt type medium layers to the MR head.
Also, another idea that a Cu film having a thickness of 2000 is arranged between a Cr film arranged under a Co type alloy magnetic film and a substrate to reduce a medium noise of a medium is disclosed in the Published Unexamined Japanese Patent Application No. H4-134618 (134618/1992). In addition, another idea that a Cu film having a thin thickness is arranged between a Cr layer arranged under a magnetic film and a substrate to heighten a coercive force of a medium is disclosed in the Published Unexamined Japanese Patent Application No. H6-96431 (96431/1994).
Also, another idea that a medium is produced by dividing a Co-group alloy medium layer into a plurality of divided layers through Cu layers to alternately arrange the divided layer and the Cu layer is disclosed in the Published Unexamined Japanese Patent Application No. S59-142744 (142744/1984). In this idea, upper divided layers of the Co-group alloy medium layer are used as read and write layers (R/W layers), and lower divided layers of the Co-group alloy medium layer are used as a marker signal for positioning a head. Therefore, the configuration of the medium is determined without considering the formation of the medium having a low medium noise and a high recording density. In this case, a film thickness of each Cu layer ranges from 0.2 to 0.8 .mu.m to avoid the interference between recorded information in the upper divided layers and recorded information in the lower divided layers.
However, even though the Cu layers having the above-described thickness are arranged between a Cr backing layer and a substrate, a medium noise cannot be sufficiently reduced during a recording or reproducing operation, and information cannot be sufficiently recorded in a high recording density in a magnetic recording drive.